Avoid re-iterate out-of-order display items

Source/platform/graphics/paint/DisplayItemList.h

Index: Source/platform/graphics/paint/DisplayItemList.h
diff --git a/Source/platform/graphics/paint/DisplayItemList.h b/Source/platform/graphics/paint/DisplayItemList.h
index a6780c4ef636ec2561e1f1cc0e596c5edf6bc746..ea3ad1b11ace8ecf07f55088e74860d0a826f3c0 100644
--- a/Source/platform/graphics/paint/DisplayItemList.h
+++ b/Source/platform/graphics/paint/DisplayItemList.h
@@ -141,8 +141,10 @@ private:
 
     static size_t findMatchingItemFromIndex(const DisplayItem::Id&, const DisplayItemIndicesByClientMap&, const DisplayItems&);
     static void addItemToIndexIfNeeded(const DisplayItem&, size_t index, DisplayItemIndicesByClientMap&);
-    DisplayItems::iterator findOutOfOrderCachedItem(DisplayItems::iterator currentIt, const DisplayItem::Id&, DisplayItemIndicesByClientMap&);
-    DisplayItems::iterator findOutOfOrderCachedItemForward(DisplayItems::iterator currentIt, const DisplayItem::Id&, DisplayItemIndicesByClientMap&);
+
+    struct OutOfOrderIndexContext;
+    DisplayItems::iterator findOutOfOrderCachedItem(DisplayItems::iterator currentIt, const DisplayItem::Id&, OutOfOrderIndexContext&);
+    DisplayItems::iterator findOutOfOrderCachedItemForward(const DisplayItem::Id&, OutOfOrderIndexContext&);
     void copyCachedSubtree(DisplayItems::iterator& currentIt, DisplayItems& updatedList);
 
 #if ENABLE(ASSERT)